This invention relates to a process for preparation of 6-halopenicillanic esters and 7-halocephalosporanic esters. These compounds are valuable as intermediates for conversion to 6-methoxypenicillanic esters and 7-methoxycephalosporanic esters. The acids of said methoxy-.beta.-lactam compounds possess desirable antimicrobial properties.
Since the prediction by J. L. Strominger and D. J. Tipper, Amer. J. Med. 39, 708 (1965), that 6-methylpenicillins and 7-methylcephalosporins should have enhanced microbiological activity and the recent discovery of the 7-methoxycephalosporins obtained from the fermentation of Streptomycete organisms by R. Nagarajan, et al., J. Amer. Chem. Soc., 93, 2308 (1971), considerable interest has developed in the synthesis of .beta.-lactam antibiotics having a substituent .alpha. to the .beta.-lactam carbonyl of the penicillin and cephalosporin antibiotics.